Use of a reactive, or reducing gas as a method to increase contact lifetime in micro contact mems switch devices

ABSTRACT

A MEMS device comprises an electro mechanical element in a sealed chamber containing a gas comprising a reactive gas selected to react with any contaminants that may be present or formed on the operating surfaces of the device in a manner to maximize the electrical conductivity of the surfaces during operation of the device. The MEMS device may comprise a MEMS switch having electrical contacts as the operating surfaces. The reactive gas may comprise hydrogen or an azane, optionally mixed with an inert gas, or any combination of the gases. The corresponding process provides a means to substantially reduce or eliminate contaminants present or formed on the operating surfaces of MEMS devices in a manner to maximize the electrical conductivity of the surfaces during operation of the devices.

FIELD OF THE INVENTION

The present invention relates to micro-electro-mechanical system (MEMS)devices, such as MEMS switches, and in particular to controllingactuation of MEMS switches to improve performance.

BACKGROUND OF THE INVENTION

The “silicon revolution” drove the development of faster and largercomputers beginning in the early 1960's giving rise to predictions ofrapid growth because of the increasing numbers of transistors packedinto integrated circuits with estimates they would double every twoyears. (“Moore's Law”) Since 1975, however, they doubled about every 18months.

An active period of innovation in the 1970's followed in the areas ofcircuit design, chip architecture, design aids, processes, tools,testing, manufacturing architecture, and manufacturing discipline. Thecombination of these disciplines brought about the VLSI era and theability to mass-produce chips with 100,000 transistors per chip at theend of the 1980's, succeeding the large scale Integration (“LSI”) era ofthe 1970's with only 1,000 transistors per chip. (Carre, H. et al.“Semiconductor Manufacturing Technology at IBM”, IBM J. RES. DEVELOP.,VOL. 26, no. 5, September 1982). Mescia et al. also describe theindustrial scale manufacture of these VLSI devices. (Mescia, N.C. et al.“Plant Automation in a Structured Distributed System Environment,” IBMJ. RES. DEVELOP., VOL. 26, no. 4, (July 1982).

The release of IBM's Power6™ chip in 2007, noted “miniaturization hasallowed chipmakers to make chips faster by cramming more transistors ona single slice of silicon, to the point where high-end processors havehundreds of millions of transistors . . . .”(http://www.nytimes.com/reuters/technology/tech-ibm-power.html?pagewanted=print(Feb. 7, 2006))

More recently, “engineers did a rough calculation of what would happenhad a 1971 Volkswagen Beetle improved at the same rate as microchips didunder Moore's Law: ‘Here are the numbers: [Today] you would be able togo with that car 300,000 miles per hour. You would get two million milesper gallon of gas, and all that for the mere cost of 4 cents!’” T.Friedman, N.Y. Times, Op Ed, May 13, 2015.

Technology scaling of semiconductor devices to 90 nm and below hasprovided many benefits in the field of microelectronics, but hasintroduced new considerations as well. Smaller chip geometries result inhigher levels of on-chip integration and performance, higher current andpower densities, increased leakage currents, and low-k dielectrics allof which present new challenges to package designs.

Components fabricated with microelectromechanical systems (MEMS) arebeing incorporated in an increasing number of consumer applicationsincluding, but not limited to, automotive electronics, medicalequipment, cell phones, hard disk drives, computer peripherals, andwireless devices. MEMS technology is directed at forming miniaturizedelectro-mechanical devices and structures using microfabricationtechniques. MEMS devices are characterized by some form of mechanicalfunctionality, which is typically in the form of a least one movingstructure. Structures may be formed on a suitable substrate by a seriesof processing steps involving thin film depositions that arephotolithographically masked and etched. MEMS mechanical elements,sensors, and actuators may be integrated on a common substrate withcomplementary metal-oxide-semiconductor (CMOS) devices.

Fabricators manufacture MEMS devices using processes and equipmentdeveloped for standard semiconductor integrated circuit chips, whichallowed for microfabrication with increased precision, smaller devices,and generally devices having lower power requirements. One type of MEMSdevice that has wide applicability in the electronics industry comprisesthe MEMS switch which evolved from the increased need for miniatureswitches on semiconductor substrates along with other semiconductorcomponents to form various types of circuits.

These miniature switches can act as relays and in many instancesreplaced field effect transistor switches (FETS) in microcircuits.Manufacturers employed MEMS switches to reduce insertion losses due toadded resistance as well as parasitic capacitance and inductanceinherent in FETS in a signal path. MEMS switches also find use in manyradio frequency (RF) applications, such as antenna switches, loadswitches, transmit or receive switches, tuning switches, and the like.Some applications utilize multiple MEMS switches, with each havingspecific electrical requirements, mechanical requirements, or both.These applications require consistency of electrical characteristics ormechanical characteristics, or both.

MEMS switches rely on mechanical movement of a deflection electrode tomake or break contact with a stationary electrode, thus forming a shortcircuit or an open circuit depending on the position of the deflectionelectrode. MEMS switches are typically actuated by using electrostaticforces to produce the mechanical movement required to change the stateof the switch. MEMS switches are noted for their low power consumption,high isolation in the off state, low insertion loss in the on state, andhigh linearity, typically outperforming switches relying onsemiconductor devices such as field-effect transistors (FETs). Switchesprovide an important building block in many electronic systems, and theperformance characteristics of MEMS switches make them particularlyattractive for providing signal switching functions in mixed signal,communications, and radio frequency integrated circuit applications.

One of the devices comprise MEMS-based relays for application in radiofrequency (“RF”) communication technologies because the switchingcharacteristics of a MEMS relay is superior to those of traditionalswitches like the GaAs MESFET, and the p-i-n diode. For example, MEMSrelays have lower power consumption rates, lower insertion losses, andhigher linearity. All these features make MEMS relays a great candidatefor wireless communication applications like wireless transceivers incellular phones.

MEMS switches require large voltages to actuate the switch. Fabricatorsterm this as a “pull-down,” or “pull-in,” or actuation voltage, which isanywhere from 20 to 40 volts or more. A typical MEMS switch useselectrostatic force to cause mechanical movement that result inelectrically bridging a gap between two contacts such as in the bendingof a cantilever. In general this gap is relatively large in order toachieve large impedance during the “off” state of the MEMS switch.Consequently, this large pull-down voltage electrically bridges thelarge gap, while a smaller maintaining voltage maintains the bridge.These high pull-down voltages can cause arcing and consequent oxidationin the switch which contributes to its eventual breakdown. Even so, atypical MEMS switch has a useful life of approximately 10⁸ to 10⁹cycles, but fabricators nonetheless have an interest in increasing thelifetime of these switches.

MEMS microswitches, including those with very low contact forces, arealso very sensitive to any organic or other contamination occurring onthe contact surfaces. Therefore, these switches are typically packagedor sealed as early as possible in the manufacturing process in an inertambient environment. This environment is typically a mixture of inertgases such as N₂, Ar and the like, where the pressure vary betweenatmospheric pressure and higher. For larger switches, such as relays,getters are commonly used within the package to accumulate anycontamination which may arise in the package. This method works verywell for larger packages, but for micro-scale switches such as MEMSswitches, including a getter within the package may be very challengingif not impossible for small cavities created in fabricating theswitches. Therefore, a clean environment consisting of an inert gas suchis typically employed in the small cavity.

RELATED ART

The following references relate to the state of the art in the field ofMEMS device manufacturing, including MEMS switches: WO2008110389A1; USxx2,0090115565; U.S. Pat. No. 4,348,566; JP5516994B2; JP05174660A;GB1399014; GB1032722A; CH351337A; and DE1020735B.

SUMMARY OF THE INVENTION

Not only do the written description, claims, drawing, and abstract ofthe disclosure set forth various features, objectives, and advantages ofthe invention and how they may be realized and obtained, but thesefeatures, objectives, and advantages will also become apparent bypracticing the present invention. This comprises structures, articles ofmanufacture, processes, and products produced by these processes thataddress the forgoing needs to not only provide advantages over therelated art, but also substantially obviate one or more of the foregoingand other limitations and disadvantages of the related art. We do thiswith our invention which comprises a MEMS device such as a MEMS switchincorporating a reactive or reducing gas that will react with anypossible organic or other contamination accumulating or occurring on thesurface of the micro-contacts of the switch during activation toincrease contact lifetime of these micro-contacts in the MEMS switchdevices.

BRIEF DESCRIPTION OF THE DRAWING

The accompanying drawing is not necessarily drawn to scale butnonetheless sets out the invention, and is included to illustratevarious embodiments of the invention, and together with thisspecification also serves to explain the principles of the invention.The drawing comprises a FIGURE illustrating a side elevation incross-section of one type of a MEMS device of the invention, e.g., aMEMS switch.

DETAILED DESCRIPTION OF THE INVENTION

To achieve the foregoing and other advantages, and in accordance withthe purpose of this invention as embodied and broadly described herein,the following detailed description comprises examples of the inventionthat can be embodied in various forms. The specific processes,compounds, compositions, and structural details set out herein not onlycomprise a basis for the claims and a basis for teaching one skilled inthe art how to employ the present invention in any novel and useful way,but also provide a description of how to make and use this invention.The written description claims, drawing, and abstract of the disclosurethat follow set forth various features, objectives, and advantages ofthe invention and how they may be realized and obtained. Again, thesefeatures, objectives, and advantages will also become apparent bypracticing the invention.

MEMS switches with very low contact forces are very sensitive to anyorganic or other contamination occurring on the contact surfaces. Highcontact forces reported for MEMS switches are typically in the mN region(i.e ˜50 mN for the OMRON switch), whereas a normal contact force may beconsidered in the 10-hundreds of micro-Newton range. Very low contactforce may be considered at ˜1 uN and lower. J. Oberhammer and G Stemme,Active Opening Force and Passive Contact Force Electrostatic Switchesfor Soft Metal Contact Materials, JMEMS, Vol. 15 No. 5, October 2006,describe this and report findings in Table 1. For the purpose of thepresent invention, we may employ contact forces in a range <100 uN.Therefore, these switches are typically packaged or sealed as early aspossible in the manufacturing process in an inert ambient environment.This environment is typically a mixture of inert gases such as N₂, Arand the like and the pressure vary between atmospheric pressure andhigher. For larger switches, such as relays, getters are commonly usedwithin the package to accumulate any contamination which may arise inthe package. This method works very well for larger packages, but formicro-scale MEMS devices or switches, including a getter within thepackage may be very challenging, if not impossible for small cavitiescreated during fabrication of switches. Therefore, a clean environmentwith an inert gas is typically employed within the small cavity.

The invention comprises, inter alia, an article of manufacture and aprocess for overcoming these and other related art difficulties by usinga reactive or reducing gas that will react with any possible organic orother contamination accumulating or occurring on the surface of themoving parts of a MEMS device such as micro-contacts of a MEMS switch.By using a reactive or reducing gas within the package of a sealedmicro-switch the lifetime of the contact surfaces may be increased. Thereactive or reducing gas will react with any organic or inorganiccontamination accumulating or forming on the contact surfaces which maycompromise the switch lifetime or performance. This approach isdifferent from using a getter placed strategically in the devicepackage, but not on the contact surfaces of the moving parts of a MEMSsuch as the contact points in a MEMS switch. The reactive or reducinggas, however, will react with any possible contaminant on, or forming onthe contact surfaces of a MEMS device such as a MEMS switch. Duringsealing, or packaging of the MEMS device, rather than using only aninert gas to remain in the cavity or package, the invention comprisesintroducing a reactive or reducing gas into and then sealing it in thecavity or package of a MEMS device.

The reactive or reducing gas comprises a gas that will react withcontaminants ordinarily found in MEMS devices such as MEMS switches.These contaminants may comprise organic or other residues, e.g.,inorganic residues that may remain in the device after manufacturing orthat are generated during use of the device. In one embodiment of theinvention these gases comprise inorganic reactive gases or reducinggases. The organic contaminants residues remnant from the MEMSfabrication process, comprise for example, photoresists or solvents, oratmospheric sources. Inorganic residues or contaminants can be oxidesformed on the switch contact surfaces during use of the MEMS device.

The reactive or reducing gas in one embodiment comprises an inorganicgas, i.e., a gas that does not contain carbon. In a further embodimentthe reactive or reducing gas comprises compounds or compositions ofmatter that maybe gaseous over a range of temperatures such as roomtemperature (20° C.) or below up to the manufacturing temperature of theMEMS device or up to the temperature developed within the MEMS devicewhen in use and slightly higher, e.g., any where from about 2° C. toabout 20° C. higher than the operating temperature of the MEMS device.

In a further embodiment these reducing gases may comprise inorganicgases, e.g., hydrogen and nitrogen hydrides also referred to as azaneswhich include, inter alia, a homologous series of inorganic compoundswith the general chemical formula NnHn+2, where n=1˜7. In one embodimentwe employ azanes, e.g., azanes which are not the explosive azanes knownin the art. Some members of the azanes in this regard (in terms ofnumber of nitrogen atoms) comprise ammonia, NH₃; diazane (or hydrazine),N₂H₄; triazane, N₃H₅; tetrazane or tetraazane, N₄H₆; pentazane orpentaazane, N₅H₇; hexazane or hexaazane, N₆H₈; heptazane or heptaazane,N₇H₉; and the like, especially those that conform to the foregoingcriteria. In another embodiment, we select the reactive gas so that thereactive process taking place at the contact surfaces may not leave anyresidual material or any substantial amount of residual material at thecontact surfaces which again may cause contamination. In a furtherembodiment we select the reactive gas so that if the byproduct/residuefrom the reduction process has a charge, it may be concentrated in theregion where the electrostatic field in the switch is the greatest (theactivator 18 in the FIGURE) and by this approach ensure that the residueis not accumulated near the contact surface, which typically does nothave a charge across it.

Because of the flammable nature of hydrogen and of some of the otherreactive gases, in one embodiment we from a mixture of an inert gas suchas nitrogen or a noble gas with the reactive gas in an amount to reducethe flammability either in manufacturing the MEMS device or use of theMEMS device. We also employ the inert gas to control the reaction rateof the reactive gas, especially the reactive gas in the sealed chamber,and any exotherm that may result from reaction of the reactive gas,especially any exotherm that may result from reaction of the reactivegas with any contaminants. The noble gases include the Group VIIIA gasesof the Periodic Table of the Elements, e.g., He, Ne, Ar, Kr, and Xe.Although falling within the Group VIIIA gases, we do not include Rn asone of the enumerated noble gases because of its radioactivity. Theinert gas can be mixed with the reactive gases where the mixture ofinert gas and reactive gas may comprise mixtures of from trace amountsup to about 90 mol percent of one gas and the balance, the other gas,where the trace amount may be about 500 ppm on a molar basis. The inertgas or can also be mixed with the reactive gas where the mixture ofinert gas and reactive gas may comprise mixtures of from about one molpercent up to about 90 mol percent of one gas and the balance the othergas.

Lastly, we may also employ combinations of reactive gases andcombinations of optional inert gases, such as the two component, threecomponent or four component combinations or more of each of these gases.

The FIGURE illustrates a side elevation in cross-section of a MEMSswitching device 10 in an open position comprising an electricallyconductive flexible switching arm 12 movable toward electrical conductor16 in the direction shown by arrow 13. Arm 12 connects to electricalconductor 14 to provide electrical current through the circuit formed byarm 12 and electrical conductors 14 and 16 when arm 12 is brought intocontact with conductor 16 by means of activator 18. Arm 12 in thisregard is moveable in the direction of arrow 13 by means of anelectrostatic force provided by activator 18 to develop a “pull-down,”or “pull-in,” or actuation voltage anywhere from about 20 to about 40volts or more. The electrostatic force causes mechanical movement inflexible switching arm 12 in the direction of arrow 13 that results inclosing the gap between the operating surface or contact surface 12C onthe end of flexible switching arm 12 and the operating surface orcontact surface 16C on electrical conductor 16 so that surface 12C is inelectrical contact with surface 16C when the MEMS switching device 10 isin the “on” position. Opening and closing the gap between the surfaces12C and 16C causes electrical arcing between them that in turn causes areaction of any organic or inorganic materials in the device 10 thatproduce contaminant reaction products that deposit on the surfaces andimpedes electrical conductivity between them. The reactive gas orreducing gas combines with or reacts with the contaminant reactionproducts substantially removing them from the surfaces or otherwisesubstantially maximizing the electrical conductivity of the surfaces.

Housing 20 encloses switching arm 12, electrical conductor 14, andelectrical conductor 16, providing a chamber 22 that contains thereactive or reducing gas. Again, this reactive or reducing gassubstantially maximizes electrical conductivity, i.e., substantiallyrestores or substantially reverses lost electrical conductivity of thecontact surface 12C and/or the contact surface 16C during day-to-dayoperation of MEMS switching device 10 and over the lifetime of operationof MEMS switching device 10. Substrate 24 supports the foregoingelements. In one embodiment, substrate 24 may comprise a semiconductorstructure known in the art with conductors 14 and 16 operativelyassociated with it, e.g., electrically connected to it. Overmold 26envelops the device 10.

Related art describes the manufacture MEMS devices, as for example U.S.Pat. Nos. 7,735,216; 7,710,059; 7,616,889; 7,427,846; 7,336,900;6,429,755; 6,391,674; 6,275,122; and 6,238,946. Related art alsodescribes MEMS switches and methods for their manufacture in U.S. Pat.Nos. 9,019,049; 8,829,626; 8,791,778; 8,748,207; 8,609,450; 8,604,898;8,451,077; 8,445,306; 8,211,728; 7,726,010; 17,657,995; 7,602,265;7,581,314; 7,348,870; 7,202,764; and 6,744,338. U.S. Pat. No. 7,999,643describes MEMS switches that incorporate gases in their interiors andmethods for their manufacture. We can manufacture the MEMS devices orMEMS switches of the invention in accord with any one or combination ofthe foregoing disclosures, e.g., the foregoing disclosures in the publicrealm.

Throughout this specification, and abstract of the disclosure, theinventors have set out equivalents, of various materials as well ascombinations of elements, materials, compounds, compositions,conditions, processes, structures and the like, and even though set outindividually, also include combinations of these equivalents such as thetwo component, three component, or four component combinations, or moreas well as combinations of such equivalent elements, materials,compositions conditions, processes, structures and the like in anyratios or in any manner.

Additionally, the various numerical ranges describing the invention asset forth throughout the specification also includes any combination ofthe lower ends of the ranges with the higher ends of the ranges, and anysingle numerical value, or any single numerical value that will reducethe scope of the lower limits of the range or the scope of the higherlimits of the range, and also includes ranges falling within any ofthese ranges.

The terms “about,” “substantial,” or “substantially” as applied to anyclaim or any parameters herein, such as a numerical value, includingvalues used to describe numerical ranges, means slight variations in theparameter or the meaning ordinarily ascribed to these terms by a personwith ordinary skill in the art. In another embodiment, the terms“about,” “substantial,” or “substantially,” when employed to definenumerical parameter include, e.g., a variation up to five per-cent, tenper-cent, or 15 per-cent, or somewhat higher. Applicants intend thatterms used in the as filed or amended written description and claims ofthis application that are in the plural or singular shall also beconstrued to include both the singular and plural respectively whenconstruing the scope of the present invention.

All scientific journal articles and other articles, including internetsites, Information Disclosure Statements as well as issued and pendingpatents that this written description or applicants' InventionDisclosure Statements mention, including the references cited in suchscientific journal articles and other articles, including Internetsites, and such patents, are incorporated herein by reference in theirentirety and for the purpose cited in this written description and forall other disclosures contained in such scientific journal articles andother articles, including internet sites as well as patents and thereferences cited therein, as all or any one may bear on or apply inwhole or in part, not only to the foregoing written description, butalso the following claims, drawing, and abstract of the disclosure.

Although we describe the invention by reference to some embodiments,other embodiments defined by the doctrine of equivalents are intended tobe included as falling within the broad scope and spirit of theforegoing written description, and the following claims, abstract of thedisclosure, and drawing.

1-10. (canceled)
 11. A process for substantially reducing contaminantsin a MEMS device comprising a sealed chamber containing an electromechanical element having operating surfaces, by placing a gas in saidchamber comprising a reactive gas selected to react with anycontaminants that may be present or formed on the operating surfaces ofsaid device in said sealed chamber in a manner to maximize theelectrical conductivity of said operating surfaces during operation ofsaid MEMS device.
 12. The process of claim 11 wherein said MEMS devicecomprises a MEMS switch and said operating surfaces compriseelectrically conductive switch contact surfaces in said MEMS switch. 13.The process of claim 11 wherein said reactive gas comprises a reducinggas.
 14. The process of claim 12 wherein said reactive gas comprises areducing gas.
 15. The process of claim 11 wherein said reactive gascomprises hydrogen or an azane or combinations thereof.
 16. The processof claim 14 wherein said reducing gas comprises hydrogen or an azane orcombinations thereof.
 17. The process of claim 11 wherein said reactivegas is optionally mixed with an inert gas to control the reactivity ofsaid reactive gas.
 18. The process of claim 12 wherein said reactive gasis optionally mixed with an inert gas to control the reactivity of saidreactive gas.
 19. The process of claim 11 wherein said reactive gascomprises hydrogen, optionally mixed with an inert gas to control thereactivity of said reactive gas, wherein said inert gas comprisesnitrogen or a noble gas or any combination of said reactive gas with anycombination of said optional said inert gas.
 20. The process of claim 12wherein said reactive gas comprises hydrogen, optionally mixed with aninert gas to control the reactivity of said reactive gas, wherein saidinert gas comprises nitrogen or a noble gas or any combination of saidreactive gas with any combination of said optional inert gas. 21-30.(canceled)
 31. The process of claim 15 wherein said azane reactive gascomprises a non-explosive azane selected from a homologous series ofinorganic compounds with the general chemical formula NnHn+2, wheren=1˜7 or combinations thereof.
 32. The process of claim 16 wherein saidazane reactive gas comprises a non-explosive azane selected from ahomologous series of inorganic compounds with the general chemicalformula NnHn+2, where n=1˜7 or combinations thereof.
 33. The process ofclaim 15 wherein said azane reactive gas comprises ammonia, diazane,triazane, tetrazane, pentazane, hexazane, or heptazane, or combinationsthereof.
 34. The process of claim 16 wherein said azane reactive gascomprises ammonia, diazane, triazane, tetrazane, pentazane, hexazane, orheptazane, or combinations thereof.
 35. The process of claim 31 whereinsaid reactive gas is optionally mixed with an inert gas to control thereactivity of said reactive gas.
 36. The process of claim 32 whereinsaid reactive gas is optionally mixed with an inert gas to control thereactivity of said reactive gas.
 37. The process of claim 31 whereinsaid reactive gas is optionally mixed with an inert gas to control thereactivity of said reactive gas, wherein said inert gas is selected fromnitrogen or a noble gas and combinations thereof.
 38. The process ofclaim 11 wherein said reactive gas is selected to remove saidcontaminants on said operating surfaces.
 39. The process of claim 11wherein the reactive gas is selected so that any reactive process takingplace at the contact surfaces may not leave any substantial amount ofresidual material at the contact surfaces which may cause contamination.40. The process of claim 11 wherein any byproduct/residue resulting fromsaid reactive gas reacting in said MEMS has a charge so that saidreactive gas may be concentrated in the region of said MEMS device whereany electrostatic field in the device is the greatest to ensure that anyresidue generated during the operation of said MEMS device is notaccumulated near any of said operating surfaces that do not have acharge across it.